Frequency analyzer



May 8, 1956 R. F. slMoNs FREQUENCY ANALYZER Filed Feb. 2, 1955 TML- 1.2L

ATTO -4/ E s United States Patent O FREQUENCY ANALYZERv Rodney F. Simons, Huntington, N. Y., assignor., by mesne assignments, to the United States of America as represented bythe Secretary of the Navy Application February 2, 1955, Serial No. 485,831

4 Claims. (Cl. 315-1) This invention relates to a frequency analyzer and more particularly to a frequency analyzer utilizing a wedge-shaped piezoelectric crystal.

Wedge-shaped piezoelectric crystals having given length and width dimensions and a thickness dimension which varies from a minimum value at one end to a maximum value at the other end, are well known in the art. Such crystals will resonate at different frequencies along the length thereof, the resonant frequency being determined by the thickness of the crystal at any point. Thus lthey will resonate at a minimum frequency at the end having maximum thickness, maximum frequency at the end having minimum thickness and at intermediate frequencies between the two ends. If the maximum thickness of the crystal is not greater than 1A@ of the width of the crystal, the amplitude as well as the resonant frequency of oscillation will depend only upon the distance from the ends of the crystal and will be constant over the width of the crystal.

Briefly, this invention contemplates utilizing a wedgeshaped crystal, of the character described above, in a cathode ray tube to produce deflections in the electron beam of the cathode ray tube, the locations of which are indicative of the frequency components of a complex signal applied to the crystal.

It is therefore an object of this invention to provide a frequency analyzer, wherein the frequency components of a complex signal are indicated by the locations of deflections in a frequency base line appearing on the face of a cathode ray tube.

It is a further object of this invention to provide a frequency analyzer which utilizes a wedge-shaped crystal for deflecting the electron beam of a cathode ray at points along the length of the crystal which are resonant at the frequencies of the components of a complex signal applied to the crystal.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. l is a block diagram of a cathode ray tube incorporating a wedge-shaped crystal assembly and the associated circuitry connected to the cathode ray tube; and

Fig. 2 is a diagrammatic view of the crystal assembly and the electron beam.

Referring now to Fig. l, there is shown cathode ray tube 102 including electron gun 104, deflecting plates 108 and 106, and fluorescent screen 110. Wedge-shaped crystal assembly 112 is located within cathode ray tube 102 in between deflecting plates 106 and 108 and uorescent screen 110.

Operating potentials are applied to electron gun 104 from voltage supply 114 in a conventional manner to produce an electron beam therefrom. The output of saw-tooth-wave generator 116 is applied to deflection plates 106 and 108 for linearly deilectng the electron ICC beam. Although not shown, means for forming the electron beam into a thin sheet may be substituted for deflection plates 106 and 108 and saw-tooth-wave generator 116. In either case the electron beam passes in proximity to crystal assembly 112 and forms a luminescent line on fluorescent screen 110. The output of complex R. F. signal source 118 is applied as an input to crystal assembly 112.

Referring now to Fig. 2, piezoelectric crystal wedge 202 has its under surface in contact with electrode 204. Electrode 204 entirely covers the under surface of crystal wedge 202. The upper surface of crystal wedge 202 is in contact with electrode 206. Electrode 206 has a length equal to that of crystal wedge 202, but a width which is only a fraction of that of crystal wedge 202, so that electrode 206 covers only a portion of the upper surface of crystal wedge 202.

Located above electrode 206 and in spaced relation ship therewith is cancelling plate 208. Cancelling plate 208 is oriented substantially parallel to the upper surface of crystal wedge 202.

Variable capacitance 210 in shunt with resistor 212 connects cancelling plate 208 to electrode 204. Cancelling plate 208 is coupled to electrode 206 by interelectrode capacitance 214. Crystal wedge 202 is oriented with its width substantially parallel to the direction of electron beam 216. Electron beam 216 passes between upper electrode 206 and cancelling plate 208.

The complex R. F. signal which is to be analyzed is connected between electrodes 204 and 206.

Referring now to the operation of the disclosed frequency analyzer, the application of the complex R. F. signal between electrodes 204 and 206 causes crystal wedge 202 to oscillate at those discrete points along the length thereof which are resonant at the respective frequency components of the complex signal.

Interelectrode capacitance 214 and variable capacitance 210 form a voltage divider which applies a portion of the complex R. F. signal to cancelling plate 208. Resistor 212 merely provides a direct current return for electrons of electron beam 216 which happened to impinge upon the cancelling plate 208. The potential difference existing between electrode 206 and cancelling plate 208 produces a first electric field perpendicular to electron beam 216 in the region over the portion of the width of crystal wedge 202 covered by electrode 206. The potential difference existing between electrode 204 and cancelling plate 208 produces a second electric field perpendicular to electron beam 216 in the region over the portions of the width of crystal wedge 202 which are not covered by electrode 206. These first and second electric fields are oppositely directed; that is, if one points upward the other points downward. There fore electron beam 216, which passes through both the first and second electric field first will be deflected in one direction and then will be deflected in the opposite direction.

The amount of deflection provided by each electric field is proportional to the intensity of that electric field and the extent thereof through which electron beam 216 passes. The average relative intensity of the first and second electric fields depends on the setting of variable capacitance 210. However, there will be local variations in the intensity of the electric fields in the vicinity of those points on crystal wedge 202 which are resonant at the frequency components of the complex R. F. signal applied thereto.

Therefore, by setting variable capacitance 210 at a point such that in the vicinity of points on crystal wedge 202 which are non-resonant at the frequency components of the complex R. F. signal applied thereto, the deflection experienced by electron beam 216 in passing through the tirst electric iield'is equal to the deflection experienced'-V by4 electronbeamA 216 in passing" throughl the second electric field, the only resultant deections in electron beam 216 will take place in the vicinity of thoseipoints on crystal'wed'ge 202 which are resonant at the frequency components o" theA complex R11 F.' signal; Thus the luminescent line formed'on-uores: cent` screen H0 of cathode ray tube 102" by electron beam' 216 will be deflected at a plurality of points, the position of which is indicative of the frequencies containediin the'respective components of Athe complexY Ri F. signal.

Obviously manyY modifications and variationsof lthe. present invention arepossib'le in thelight ofjth'e above.V teachings;v It isi therefore to be' understood' that within,

the` scope` of the appended claims the invention may be practiced otherwisel than as specifically described.'

Iclaim:Y l.' In combination -with a cathode ray tube having an electron gun for forming an electron beamand a uorescent face on Which said'el'ectron beam impinges;

first'meansA for deecting said electron beam along one dimensionh ofthe face ofsaid cathode ray tube; awedgeshaped piezoelectric' crystalA having a given. length, a givenvwidth and a thickness which varies monotonically. alongthe`-1ength thereof from a given minimum thick-r ness; to a given` maximum thickness, saidmaximurn thickness'being small" relative to the width of saidcrystal, and'said'crystal' being oriented within said'vcathode ray-tube between said'electron gun and said" face with the lengththereof substantially parallelto said one dif mension and the Width thereof substantially parallel to said electron beam; saidelectron beam passing in proximityy to said crystal; a rst electrode in contact with one. length-Width surface of said crystal and a second electrode incontact with the other length-width surface of said, crystal; second means for applying a complex` signal between said rst and second electrodes, whereby:

said complex signal-tends: to deect saidfelectronsbeam in av direction perpendicular to said one dimension; and` third means in spaced relationship with respect to said crystal forcancelling the tendency of said complexl signal to deect said electrorrrbeam at all points along the length of said crystal which are non-resonant to frequency components of said complex signal.

2. The combination in accordance with claim l, wherein said first electrode covers the,` entire length and width of said surface ofv said crystal, saidsecond electrode covers the entirel length but only a portionl of the width of said second surface of Asaid crystal,v andwhereinsaidt:

third means comprises ametallic platee havinguaslength; and width at least equal to the, correspondingdimene. sions of said. crystal, said. third means being oriented in fixed space relationship over said"second" surface of said crystal and substantiallyparallelthereto, and fourth means coupled to said second means for applying a given portion of said complex signal to said metallic plate, said electron beamv passing between said second. surface of :saidcrystal and said-metallic plate;

3i The-combinationin'accordance-With claim 2A," Where-` in said fourth means comprises a capacitance. voltage: dividere comprisingy theu interelectrode, capacitance between4 said second-electrode and-said metallic' plate and" a lumped" variable capacitance connected between said metallic rplate and said' first electrode.;

4: The' combination inaccordance with-claim' 3, furtherinc'ludingl a resistor having' a high `resistance relative to thereactance of saidlumped-v capacitance: connected in shunty With said lumped capacitance for providing, a

direct current'return--forelectrons-ot` said electron beam impinging'upon said/metallic plate.

References Cited -in the file of this patenty UNITED STAT ES.V PATENTS 2,179,097 Lawl Nov.-7, 1939i 2,240,304 Koch Apr. 29', 1941 2,361,998; Fleming-Williams Nov. 7, 1944 2,600;463 BiertenY June 17; 1952' 2,634,372 Salisbury Apr: 7, 1953 Oestreicher Nov. 10, 11953" 

